1. Field of the Invention
This invention relates to an eyepiece, and more particularly to a super-wide field eyepiece.
2. Related Background Art
Generally, many of eyepieces according to the prior art are of a simple construction comprising a combination of positive lenses, and in them, Petzval sum assumes a great positive value and therefore, curvature of image field is difficult to correct and distortion becomes great.
Further, if eye relief is made great, the spherical aberration of the pupil could not be sufficiently corrected and so-called eclipse has sometimes occurred around the field of view.
The correction of these aberrations has heretofore been solved by disposing a concave surface having negative refractive power, as disclosed, for example, in U.S. Pat. No. 5,227,918.
The eyepieces according to the prior art, however, have suffered from the inconvenience that curvature of image field is greatly fluctuated by a variation in the angle of the incident principal ray (a variation in the objective side exit pupil position) resulting from a difference or a variation in an objective or a lens barrel prism system and it is difficult to keep the correction of each aberration good.